The Background of the Invention will be explained with the aid of the numbered references which appear at the end of this section of the specification. The quantification of volumetric fluid (e.g., blood) flow would be beneficial for a number of applications, including clinical applications, such as diagnosis of heart disease, cartoid stenosis, coronary arteriosclerosis, and renal failure. Doppler is the current clinical standard for measuring blood flow with ultrasound. Fluid motion towards or away from an ultrasound beam pulse modifies the wavelength of the insonifying pulse. Assuming the angle between the beam and the orientation of a fluid-carrying vessel (e.g., blood vessel) are known, the velocity of fluid flow in the vessel then is computed from the resulting Doppler frequency shift. Current techniques for volume flow measurement require a sonographer to orient the center axis of the vessel in the scan plane of the ultrasound beam, and then to calculate the total flow volume assuming a circularly symmetrical lumen. These assumptions, which are often not true, lead to large errors, making the method very difficult to apply.
The use of multiple Doppler beams to determine in-plane flow velocities (i.e., velocities in the ultrasound beam scan plane) have been known for many decades (Wang, 1982) [1]. Using two co-planar beams and trigonometric relations, the derived measured velocity is angle independent.
The cross-correlation of consecutive ultrasound A-lines eliminates the aliasing ambiguity of Doppler (Bonnefous 1986) [13].
Speckle tracking, the correlation of patterns between sequential frames, has been used to determine 1-D and 2-D flow vectors (Trahey 1987) [2]. With the development of volumetric ultrasound scans, the correlation search algorithm has been applied in 3-D with some success (Morsy 1999) [3].
One of the first techniques to quantify the magnitude of the non-axial flow components was developed by Newhouse (1987) [4] and is based on spectral broadening of the ultrasound RF signal.
More recently, Anderson (1998) [5] used a spatial weighting of the point spread function to quantify the lateral motion. In a similar study, Jensen (1998) [6] applied a transverse spatial modulation generated by apodization of the transducer elements to quantify flow in one or two directions transverse to the axial flow. Both of these techniques only determine 2-D flow.
The estimation of blood velocity using the decorrelation of echo signals has also been fairly well documented. Using the time rate-of-change of A-lines, Bamber (1988) [7] demonstrated that decorrelation could be used to image tissue motion and blood flow. More quantitatively, Li et al (1997) [8] showed that the decorrelation of RF signals was linearly related to the lateral displacement. The detection of variations in contrast-enhanced blood flow using grayscale decorrelation has also been previously shown in animal studies (Rubin, 1999) [9].
[1] Wang W, Yao L. A double beam Doppler ultrasound method for quantitative blood flow velocity measurement. Ultrasound Med Biol 1982;8:421-425.
[2] Trahey G E, Allison J W, von Ramm O T, Angle independent ultrasonic detection of blood flow. IEEE Trans Biomed Eng 1987;34:965-967.
[3] Morsy A A, von Ramm O T. FLASH correlation: A new method for 3-D ultrasound tissue motion tracking and blood velocity estimation. IEEE Trans Ultra Ferro Freq Con 1999;46:728-736.
[4] Newhouse V L, Censor D, Vontz T, Cisneros J A, Goldberg B B. Ultrasound Doppler probing of flows transverse with respect to beam axis. IEEE Trans Biomed Eng 1987;34:779-789.
[5] Anderson M E. Multi-dimensional velocity estimation with ultrasound using spatial quadrature. IEEE Trans Ultra Ferro Freq Con 1998;45:852-861.
[6] Jensen J A, Munk P. A new method for estimation of velocity vectors. IEEE Trans Ultra Ferro Freq Con 1998;45:837-851.
[7] Bamber J, Hasan P, Cook-Martin G, Bush N. Parametric imaging of tissue shear and flow using B-scan decorrelation rate (abstr). J Ultrasound Med 1988;7:S135.
[8] Li W G, Lancee C T, Cespedes E I, vanderSteen A F, Bom N. Decorrelation of intravascular echo signals: Potentials for blood velocity estimation. J Acoust Soc Am 1997;102:3785-3794.
[9] Rubin J M, Fowlkes J B, Tuthill T A, Moskalik A P, Rhee R T, Adler R S, Kazanjian S, Carson P L, Speckle decorrelation flow measurement with B-mode US of contrast agent flow in a phantom and in rabbit kidney. Radiology 1999;213;429:437.
[10] Tuthill T A, Krxc3xccker J F, Fowlkes J B, Carson P L Automated three-dimensional US frame positioning computed from elevational speckle decorrelation. Radiology 1998;209:575-582.
[11] Wear K A, Popp R L. Methods for estimation of statistical properties of envelopes of ultrasonic echoes from myocardium. IEEE Trans Med Imag 1987;6:281-291.
[12] Adler R S, Rubin J M, Fowlkes J B, Carson P L, Pallister J E. Ultrasonic estimation of tissue perfusion: a stochastic approach. Ultrasound Med Biol 1995;21:493-500.
[13] Bonnefous O, Pesque P. Time domain formulation of pulse-Doppler ultrasound and blood velocity estimation by cross correlation. Ultrasonic Imag 1986;8:73-85.
[14] Chen J, Fowlkes J B, Carson P L, Rubin J M. Determination of scan-plane motion using speckle decorrelation: theoretical considerations and initial test. Int J Imaging Syst Technol 1997;8:38-44.
[15] Chen, J R, Fowlkes J B, Carson P L, Rubin J M, Adler R S. Autocorrelation of integrated power Doppler signals and its application. Ultrasound Med. Biol. 1996; 22: 1053-1057.
The preferred embodiment is useful in an ultrasound system for measuring the volume of fluid flow within a region of interest. In such an environment, ultrasound waves are transmitted to the vessel in transmit directions defining a scan plane, preferably by an ultrasound transducer. Data signals are generated in response to ultrasound waves backscattered from the fluid within the vessel. Velocity signals having velocity values representing components of velocity of the fluid flow in the scan plane are generated in response to data generated from the data signals. Portions of the data are correlated, and the rate of decorrelation of the portions is calculated. The volume of flow of the fluid is estimated in response to the velocity signals and the rate of decorrelation. The techniques preferably are implemented with an ultrasound transducer and a data processor.
By using the foregoing techniques, the volume of fluid flow in a vessel can be determined independent of scan angle and without making any assumptions about vessel shape or flow geometry. For example, the techniques permit true blood volume flow estimates without any of the assumptions typically made with the above-described prior methods. The techniques of the preferred embodiment can be incorporated into most of the standard ultrasound transducer array scanheads now on the market. The techniques are robust and can be implemented in real time.